The invention relates to a fuel injector for a direct-injection spark-ignition internal combustion engine wherein the injector is provided with a plurality of nozzle openings arranged such that the fuel discharged therefrom forms a spray cone generating a fuel cloud.
In spark-ignition combustion engines, an inflammable fuel/air mixture is to be provided in the combustion space at the point of ignition at least in the region of the spark plug. It is known to inject fuel into a combustion chamber to form a fuel cloud in the region of the spark plug during low load engine operation. The cloud is formed only in the region of the spark plug and the engine thus can be operated with lower fuel consumption. For controlled fuel injection with a view to a controlled formation of a fuel cloud in the region of the spark plug, injectors with injection nozzles having a plurality of injection orifices are known, an individual fuel jet penetrating through each injection orifice into the combustion space. DE 39 43 816 C2 discloses a multihole nozzle for the injection of fuel, in which some of the injection orifices are designed in such a way that the fuel jets generated by them are directed into an air vortex in the combustion space, said air vortex evaporating the fuel of the injection jets and transporting it to the spark plug within the shortest possible time.
A fuel injection system for spark-ignition engines with a multihole injector is known from DE 198 04 463 A1, the injection orifices being arranged, lined up with one another, on the circumference of the injection nozzle, and a jet-managed combustion method thus being implemented as a result of the formation of a mixture cloud. The injection orifices on the circumference of the injection nozzle in this case form a conical jet, the individual fuel jets of the respective injection orifices forming a closed or coherent fuel cloud of conical form. In a known fuel injector, the injection orifices of the conical jet belt may also be arranged in two rows, with the result that the density of the outer surface area of the conical jet can be improved and consequently even larger cone angles of the conical jet can be made possible.
By means of the known arrangement of the injection orifices so as to form a conical jet, a coherent mixture cloud can be formed in the combustion space. The aim is to achieve as optimal a combustion behavior of the mixture cloud as possible with a view to as low an exhaust gas emission and as low a fuel consumption of the internal combustion engine as possible. It became clear that improved results can be achieved by means of a rapid burn-up of the mixture cloud. However, with conical fuel injection, a rapid burn-up of the mixture cloud is not possible by means of the known multihole injector. Also, in the event of deposits (carbonization) in individual injection holes in the conical jet, the flame path may be impeded by too lean a mixture in the conical cloud. Even the known arrangement of the injection holes in two rows over the circumference of the injection nozzle cannot eliminate this problem, since, at most, the thickness of the fuel-rich layer in the outer surface area of the conical cloud can be increased.
It is the object of the present invention to provide a generic fuel injector in such a way that a continuous burn-up of the fuel cloud is ensured.